HANOI — A new study has warned that if 78 hydropowerdams scheduled for construction along tributaries of the Mekong River go ahead, they will permanently block critical fish migration routes, with ‘catastrophic’ implications for the world’s biggest inland fisheries/’ target=’_blank’>fishery.

The authors, writing in Proceedings of the National Academy of Sciences, note that they have carried out the first strategic analysis of these tributary dams.

The Mekong watershed spans six countries – China, Myanmar, Laos, Thailand, Cambodia and Vietnam. Around 60 million people live along its rivers and tributaries, and many rely on fish for their livelihoods and food.

The authors made a detailed study of 27 dams where construction is planned between 2015 and 2030, to better understand implications for fish biodiversity/’ target=’_blank’>biodiversity, food security, and hydropower in the Mekong River Basin.

They found that the facilities would stop fish from migrating ‘between the river’s downstream floodplains and upstream tributaries’.

Co-author Eric Baran, a scientist at the WorldFish Center in Cambodia, said the lower part of the Mekong basin produces nearly 770,000 tons of fish per year – as much as the combined freshwater catch of Europe and South America.

He said the ‘ambitious development agendas’ of the Mekong region countries, which include plans for rapid dam construction, could threaten the food security and livelihoods of 70 per cent of the basin’s residents.

While most of the planned tributary dams will be built in Laos, the authors say effects on fish biodiversity and availability would also be felt in Cambodia and Vietnam.

In addition, the Lower Se San 2, a controversial dam planned for a tributary in Cambodia, would have ‘highly detrimental’ impacts on fish productivity, and could increase to 85 the number of endangered of fish species in the Basin system — up from 9 during the last count in 2000 — and similarly increase the number of critically endangered species to 6, up from 1 in 2000.

Other proposed mainstream dams, including Xayaburi, are subject to review by the Mekong River Commission, an advisory body founded by the four lower Mekong countries in 1995 to promote sustainable development along the river.

The authors said several planned tributary dams should also be reassessed, and also called for ‘a new regional agreement on tributary development of the Mekong River Basin’.

Ame Trandem, program director for South-East Asia at the United States-based advocacy group International Rivers, welcomed the study, saying it was the first estimate of the potential impact of the planned dams — particularly of Lower Se San 2 — on the region’s fisheries.

‘This research demonstrates a desperate need in the region to pause and rethink current hydropower plans,’ she told SciDev.Net.

‘We cannot afford to sacrifice the Mekong River’s mainstream and important tributaries simply for electricity that could easily be produced by alternative and more sustainable energy technologies.’